1. Field of the Invention
The present invention relates to a friction material to be used for an industrial machine, a railway vehicle, a cargo vehicle or an automobile and, more particularly, to an organic friction modifier to be blended into the friction material.
2. Background Art
A friction material to be used in a brake such as a disc brake or a drum brake or in a clutch is made of a friction modifier for giving a friction action and for modifying the friction performance of the friction material, a fibrous reinforcement for a reinforcing action, and a binder for binding them thereby to give a strength.
Of these, as an ingredient for adjusting friction characteristics of the friction material is exemplified by the friction modifier and a solid lubricant. These ingredients are divided into inorganic and organic ones, which have individual features so that only one kind finds it difficult to satisfy all requirements. Therefore, two or more kind of ingredients are usually used in combination. As the friction modifier, there can be enumerated an inorganic friction modifier such as alumina, silica, magnesia, zirconia, copper, aluminum or zinc, or an organic friction modifier such as rubber powder or resin powder. As the solid lubricant, there can be enumerated graphite or molybdenum disulfide. Here in the friction material of the prior art for a brake apparatus, cashew dust or the like is used as the organic friction modifier (see Patent Documents 1 and 2). The organic friction modifier such as the cashew dust is liquidified on a friction surface at a mating member temperature of about 200 to 250° C. so that it performs a lubricating action and contributes to the prevention of a wear of a mating member, the stabilization of a friction coefficient, a noise prevention or the like.
Moreover, Patent Document 3 discloses a technique for improving wear characteristics at a high temperature by using an aramid resin powder as the organic friction modifier.
[Patent Document 1]JP-A-07-11238[Patent Document 2]JP-A-2005-29653[Patent Document 3]JP-A-2002-294218
However, the cashew dust is so low in a thermal-decomposition starting temperature as to cause a reduction of a friction coefficient and an increase of the wear due to a fading phenomenon at a temperature of 300° C. or higher. Moreover, any of the organic friction modifiers made of the cashew dust or the aramid resin powder, as enumerated above, has a high static friction coefficient so that it has problems to cause easily a stick slip phenomenon and a brake noise.